What is BSP and size of a BSP thread fitting? BSP thread sizes in mm
British Standard Pipe (BSP) is an established technical standard for screw threads.BSP has been adopted internationally for interconnecting and sealing pipes and fittings by mating an external (male) thread with an internal (female) thread.
It has been adapted as standard in plumbing and pipe fitting in Australia and the Commonwealth countries.
Identify the size of a BSP thread fitting
We generally refer to a fitting by size, a 1” BSP nipple is also known as a 25mm BSP nipple but this actually refers to the inside diameter. The outside diameter for a 1” BSP fitting is not 1” or 25mm it is in fact 33.249mm at the widest point.
To identify exactly which fitting you have, measure across the thread where the red arrows are on the image below to get the “Actual Major Diameter”.
Refer to the “Actual Major Diameter” column on the chart and the corresponding columns for the BSP fitting size and the Metric size.
For example if the fitting measured 33.249 mm, it is a 1” BSP fitting or a 25mm Metric Fitting.
BSP Sizing Table
|Metric Name||BSP Name||Actual Major (Diameter in mm)||Actual Major (Diameter in inches)|
|32mm||1 1/4"||41.91 mm||1.65|
|40mm||1 1/2"||47.803 mm||1.882|
|65mm||2 1/2"||75.184 mm||2.96|
|75mm or 80mm||3"||87.884 mm||3.46|
On a side note, NPT stands for National Pipe Thread and is an American standard thread.
Happy threading! Welcome any questions & comments and if there are any other topics you would like to know more!